MAKING CHOICES: ISTOCKPHOTO.COM/SIRTRAVELALOT
Like almost everything in life, power wheelchair designs have changed…as have drive-wheel configurations. Seating and mobility teams have a wealth of
choices… so how should they decide on an optimal system for a particular client?
How Power Bases Have Changed
Historically, front-, mid-, and rear-wheel drive configurations have each had distinct
advantages and disadvantages, the latter including the fishtailing seen in frontwheel-drive power chairs and the high centering seen in mid-wheel-drive chairs.
With design evolutions, are these challenges still a concern? Are today’s power base
configurations more alike than they used to be?
Julie Piriano, PT, ATP/SMS, is VP, Clinical Education/Rehab Industry Affairs and
the Compliance Officer for Quantum Rehab.
“I don’t think the three traditional drive-wheel configurations are any more alike
today than they were in years past,” Piriano said. “However, there are more hybrid
configurations and center-of-gravity adjustments that can be made to benefit from
the advantages of two base configurations when the drive wheel is slightly forward
or rearward of the client’s center of mass. It would also be correct to say that the
engineering advancements and design evolution of modern power wheelchairs have
mitigated or at least significantly minimized many of the disadvantages of each drivewheel
configuration that were known to be true of their earlier versions.”
For example, “Fishtailing has by and large been eliminated on front-wheeldrive
chairs with enhanced electronics capabilities and the use of technology that
measures angular velocity and revolutions per minute data, senses an imbalance and
corrects it to allow the chair to move smoothly, even at higher speeds,” Piriano noted. “In addition, advanced programming and drive algorithms can
be set up to automatically slow a chair down when entering a
turn and then accelerate out of it to prevent the backend whip
that used to occur.
“The intuitive nature of driving a mid-wheel-drive chair is a
huge advantage, especially for an individual who was previously
ambulatory. But the jolting/vibratory forces that were often felt by
the end user, coupled with the concern of high centering while
negotiating obstacles and inclines, were often two significant deterrents
to recommending this drive-wheel configuration. Again, for
manufacturers that have made design innovation a priority, their
engineering teams worked the problem and created improvements
to the chassis design, suspension systems and motor technology
that significantly reduce the terrain’s effect on the end user, keep all
six wheels on the ground, and virtually eliminate these two issues.”
Improvements to Rear-Wheel Drive
That leaves rear-wheel drive, known for its longer turning radius
and often thought to be less maneuverable.
“I think a lot of us who’ve been in this industry for a long
time have gravitated toward or had a soft spot in our hearts for
rear-wheel drive,” said Brad Peterson, VP of Sales for Amylior.
“Having been with Quantum [Rehab] when mid-wheel drive was
really starting to grab more marketshare, people kind of forgot
about rear-wheel drive because of the maneuverability that the
mid-wheel drive base gave… but they forgot about why they
liked [rear-wheel drive] in the first place.”
Amylior’s version of rear-wheel drive makes many people do
a double take: “The first time I saw the Amylior R3, I [thought]
‘That’s a mid-wheel-drive chair,’” Peterson said. “You see the
casters on the ground in the rear, not an anti tip. You see the
shortened wheelbase, and it looks more mid-wheel drive.
“I think when you look at other bases — are there more
choices or less choices, is there kind of a homogenization of some
of the different technologies? — and look at the [R3], it does look
like a mid-wheel drive. But the R3 definitely has a lot of traits
that set it apart from not only rear-wheel drives, but also other
chairs that are saying they’re hybrids. The patented dual-action
suspension in Amylior products is really what makes the chair
unique, because it allows the chair to react to the ground, but
also stay amazingly stable in multiple environments, configurations
and weights. So we don’t use locks, we don’t use gas cylinders,
we don’t use any kind of a cable mechanism to give stability
to the chair. It’s just the mechanical workings of the suspension
in addition to the geometry of the chair.”
The distance from the drive wheel to the front caster, Peterson added, makes a difference: “It’s much shorter than a traditional rear-wheel-drive chair. Most rear-wheel-drive chairs have that
really big distance from the rear wheel to the front caster, which
gives them that big turning radius or that big swing. By shortening
the wheelbase and then spreading out the load over the entire
chassis, we have a very stable, very comfortable, maneuverable
chair. When people get into that chair, folks I’ve known forever
who have tried pretty much everything, they’re blown away by the
comfort of it and where it will go. It has that nice outdoor performance,
and it will go places that other chairs won’t go — but most
importantly, it’s how well it maneuvers in elevators, indoors and
how tight the turning radius can be if it’s set up correctly.”
How Technology Has Leveled the Playing Field
Tracking technology and suspension systems have improved the
overall power chair experience, regardless of drive-wheel type.
Peterson referenced Ben Leclair, a member of Amylior’s
marketing team and a professional wakeboarder who sustained a
C3 spinal cord injury in 2016. Leclair now has a mid-wheel-drive
Amylior M3 and a rear-wheel-drive R3.
“He prefers the R3,” Peterson said, “because he feels less fatigued
throughout the course of the day. He feels more comfortable in the
Hybrid Wheel Drive — that’s what we’re calling it now, an HWD,
not a rear-wheel drive. He doesn’t have as many issues with his
tone or spasticity as he does in a center-wheel drive. I think it’s the
suspension; I think it’s also where he is on the base. He’s not sitting
on top of the drive wheel; the drive wheel is kind of behind him.
Benjamin also uses a drive wheel with a 14×4″ tire, which is the larger-diameter tire for outdoor performance, and that gives him more
shock absorption as well. He’s in aggressive urban environments and
outdoors on trails, outdoors in the woods. He likes to be outdoors.”
Peterson added that while power chair literature often highlights
the big numbers — how high an obstacle a power chair can
climb, for example — consumers often have different concerns.
“People say, ‘It’s not uncomfortable for me to go over a curb
cut, it’s not annoying for me to go over a huge gap in pavement.
It’s uncomfortable and annoying for me to go over bricks,
cobblestones, those constant vibrations day to day.’ That causes
them to have more stress, more tone, more fatigue. So with the
dual-action suspension on the R3 and the M3, we have two facets
of the suspension. The first is what reacts to the ground, so that’s
what keeps your front and rear casters and your drive wheels
on the ground and helps keep them level. But the second part is
that rear spring that ties the base to the seat, so you watch that
spring absorb shock and try to keep the seat as level as absolutely
possible. When we keep the seat level, that means we’re dissipating a lot of the shock before it gets up to the consumer.That helps maintain their position and conserve energy.
“I think suspension absolutely has improved, so we’re of course
dealing with energy conservation. If someone’s not fighting against
gravity or the ride of the chair is such that they can navigate normal
obstacles without moving their body as much as they would in
older chairs, it’s going to help them stay out of bed much longer.
Maintaining a functional position by not having the body moved, not
having tone or spasticity kick in that will move them, helps them to
stay out of bed longer and helps them stay in their technology longer.”
Taking in the Whole Picture
So maybe choosing the best power chair is less about obsessing
over drivetrains and more about taking in as much information
as possible about the consumer.
“Diagnosis alone has never driven my consideration for
wheelchair base configuration, as the physical, functional, and
environmental considerations of each person are far too varied,”
Piriano said. Instead, she focuses on factors such as how the
client’s weight is distributed, the seating and accessories that will
be needed, current and future medical conditions or progressions
(ventilator, cough assist?), and how the client transfers.
Peterson agreed that details are crucial. “It’s tracking
technology,” he said. “It’s also the ability to dial in simple drive
parameters and drive settings so you’re not constantly giving those
commands to maintain a straight line. It’s also the setup of the
chair. So if the chair is set up well, where you don’t have really
aggressive caster swings or aggressive movement of the base, it’s
going to preclude the use of a lot of movements of the joystick.
“The tracking and suspension — they’re big parts, but they’re
small parts of the overall picture. It’s the caster size, it’s the caster
type. It’s where the person is centered on the chair, center of gravity
wise. It’s the cushion they’re sitting on. It’s the armrest support, it’s
the footrest support. Tracking technology and suspension are parts
that can really make it better, but they’re not the only things.”
In the end, nothing is more important than knowing the power
chair user. “Having had the benefit of working with so many different
types of power chairs and talented ATPs, there’s almost nothing we
can’t do with the technology that’s out there today,” Peterson said.
“We have the ability to do so much, from an electronics standpoint,
from a setup standpoint, from an easy setup standpoint — center of
gravity that moves, really optimizing the balance and performance of
a chair. I just hope we all take the time to ask those extra questions
that may make the difference between a chair that someone lives
in for five years and a chair that someone thrives in and finds new
independence and function for five years.”